In recent years shaving razors with various numbers of blades have been proposed in the patent literature and commercialized, as described, e.g., in U.S. Pat. No. 5,787,586, which generally describes a type of design that has been commercialized as the three-bladed Mach III razor by The Gillette Company.
Increasing the number of blades on a shaving razor generally tends to increase the shaving efficiency of the razor and provide better distribution of compressive forces on the skin but it can also tend to increase drag forces, reduce maneuverability, and reduce the ability to trim, e.g., sideburns or near the nose. U.S. Pat. No. 6,276,061, which is hereby incorporated by reference, describes locating an extra blade mounted on an angled blade support at the rear of a three-bladed razor for trimming. The patent does not describe how the blade is secured on the housing. The trimming blade is exposed such that it might potentially cut someone handling the cartridge. The patent does not describe skin contact surfaces associated with the trimming blade to control the engagement of the blade with the skin.